This invention relates to certain devices and methods for readily mounting expandable sleeves onto and dismounting expandable sleeves from printing cylinders, and more particularly to devices and methods for expandably mounting and dismounting expandable sleeves employing a pressurized fluid.
Expandable sleeves have been used in various prior art applications. For instance, in past printing operations, flexible printing plates were mounted onto the outer surface of a solid printing cylinder. These printing plates were used for printing of ink images onto a printing medium. Typically, the back of the plates were adhered directly to the printing cylinder. Since these plates were not readily interchangeable from one cylinder to another, the use of a multiplicity of printing cylinders to perform a multiplicity of jobs was required. This presented severe storage and cost problems to the end user.
Therefore, in an effort to overcome the above problems, printing sleeves were developed which were mountable onto and dismountable from printing cylinders. In order to accomplish such mounting and dismounting operations, the printing cylinders were modified at substantial cost to form an air-assisted construction capable of limited expansion of the printing sleeves.
The first patent to describe these new printing sleeves and complementary printing cylinders was U.S. Pat. No. 3,146,709. Compressed gas, generally compressed air, passing in a generally radial direction from holes located within the printing cylinders, was used to expand the sleeve to a limited extent for facilitating the mounting and dismounting operations. The outer wall of the cylinder has a slightly larger diameter than the inner wall of the sleeve, so that the sleeve will firmly frictionally fit onto the cylinder. The cylinder is hollow and has a cylindrical chamber which is used as a compressed air chamber. The printing cylinder typically comprises a cylindrical tube fitted with airtight endplates. A plurality of spaced-apart, radially-extending apertures are provided in the tube through which air from the chamber may pass for expanding the sleeve during mounting and dismounting operations. Air is introduced into the chamber through an air hose.
U.S. Pat. No. 4,144,812 and U.S. Pat. No. 4,144,813 provide non-cylindrical printing sleeves and associated air-assisted printing rolls designed in a tapered or stepped-transition configuration, the change in the sleeve or printing cylinder diameter from one end to the other being progressive, i.e., increasing or decreasing according to the direction one is moving along the printing sleeve or roll. The printing roll comprises an outer surface having one end of a diameter greater than the other longitudinal end. The printing sleeve has an inner surface designed to form an interference fit with the outer surface of the printing roll only at the designated working position, and not along the entire axial uniform cross-sectional extent of the tapered sleeve. In this case, both the tapered sleeves and the corresponding tapered cylinders must be replaced at great cost to the user.
Finally, in U.S. Pat. No. 4,089,265, a flexographic printing roll is provided comprising a rigid base tube having perforations in the form of a plurality of small apertures and a printing sleeve on the tube strained to grip the tube to retain the sleeve securely on the tube. There is no underlying printing cylinder in the conventional sense in this system.
Today, all of the prior art hollow cylinders must be modified to an air-assisted configuration in order to accommodate the mounting and dismounting operations of the expandable sleeves. Costs for such modifications range from about $60 to $200 per cylinder. Plants which employ such hollow cylinders typically have 500 to 5,000 on hand. Therefore, the cost for making such modifications can range upwards of a million dollars for larger user facilities. Furthermore, if the end user has cylinders of a solid rather than a hollow configuration, they cannot be modified to an air-assisted structure. Instead, hollow replacement cylinders must be purchased at a cost of about $1,000 per cylinder.
Complete coverage of the external air holes in the air-assisted cylinder by the sleeve is required in normal operations in all of the above-described prior art systems. Such coverage is required in order to generate an air barrier between the printing sleeve and the printing cylinder for performing the subject mounting and dismounting operations. Therefore, full-length expandable sleeves are used in all the prior art printing sleeve systems in order to maintain the requisite air barrier effect.
Therefore, a need exists for a device and a method of mounting a expandable sleeve onto non-air-assisted printing cylinders, as well as on presently existing air-assisted printing cylinders, which eliminates the prior art requirement for high cost modification of the hollow cylinders to convert them into an air-assisted configuration, and which permits the mounting and dismounting operations to be effectively conducted without the expandable sleeve completely covering the cylinder outer surface during such operations.